Process of simultaneously producing manganese metal and ferrosilicon alloy



March 28, 1961 J. L. ANDRIEUX ET AL 2,977,218

PROCESS OF SIMULTANEOUSLY PRODUCING MANGANESE METAL AND FERROSILICON ALLOY Filed Nov. 12, 1959 INVENTQRS. Jeqn Luc/en AQd/IQUX ENE/7H8 Bonn/er BY WM 92/011 9 m THE ll? ATTORNEYS PROCESS OF SHVIULTANEOUSLY PRODUCING 1XILAI)(ANESE METAL AND FERROSILICON Jean Lucien Andrieux and Etienne Leon Bonnier, Grenoble, France, assignors to Societe dElectro-Chimie dElectro-Metallurgie et des Acieries Electriques dUgine, Paris, France, a corporation of France Filed Nov. 12, 1959, Ser. No. 852,314

Claims priority, application France Nov. 22, 1958 1 Claim. (Cl. 75-80) The present application concerns a process of simultaneously producing manganese metal and ferrosilicon alloy by distillation of iron and silicomanganese mixtures under a reduced pressure and at high temperature. It also concerns various improvements to the process of French Patent No. 1,151,070 which described a process of simultaneously producing manganese metal and commercial ferrosilicon by distillation of ferromanganese and silicomanganese mixtures under a reduced pressure at high temperature. 'Ihermodynamically, this process involves the displacing of manganese with formation of iron and silicon alloys and kinetically the improving of the distillation rates of manganese due to a suitably chosen fluidity of the obtained molten alloys containing it.

Effectively, applicants have found that the iron necessary to displace the manganese from silicomanganese alloy can be used in a form other than ferromanganese and we have determined the proportions of the three elements present, manganese, iron, and silicon, necessary to remove practically all of the manganese contained in a silicomanganese alloy with simultaneous formation of ferrosilicon.

Therefore, the present invention concerns a process of simultaneously producing manganese metal and ferrosilicon alloy, which comprises mixing manganese, silicon and iron in relative proportions which will be indicated further, at least a portion of the manganese and the silicon being in the form of a silicomanganese alloy and heating this iron-manganese-silicon mixture under a reduced pressure to a temperature at which it forms a homogeneous liquid phase until the greatest part of the manganese and even, under certain conditions, all of the manganese is removed.

The relative percentages of atoms Mn, Fe, Si, which may be used in the process, will be indicated hereafter, according .to the known triangular diagram of the Mn-Fe-Si system.

At each temperature, the homogeneous liquid phase is limited by saturation curves connecting the saturation points of the respective binary systems. The figure shows the curve of the isothermal sections which corresponds to 1600 K. (1327 C.). At this temperature, the curves limiting the liquid phase comprise elements MnF, F-A, A-B, B-C, C-MnSi, MnSiMn, points A, B, C, F, representing Mn-Fe-Si compositions of the following atomic percentages:

Points Mn Fe Si 2,977,218 Patented Mar. 28, 1961 ICC eutectic of binary system Fe/Si, at 1473" K. (1200 C.). Conversely, this area is enlarged by any increase in temperature and then such points as A and B diverge from each other. At 1683 K. (1410 C.), point B joins onto point N representing the composition of iron silicide FeSi. This temperature is that of the melting point of this determined compound.

The conditions allowing favorable kinetics will therefore be fulfilled each time the composition of the mixture subjected to displacing of Mn by volatilization changes because of its impoverishing in said metal, while remaining, at the determined temperature, within the limits corresponding to the homogeneous liquid phase. The best conditions are those which permit a complete exhausting of the residue, that is, reaching the Fe-Si side of the triangle while remaining in a stability zone of the homogeneous liquid. Therefore, in the example of the figure, -i.e., at 1327 C., the ideal terminal point must be located between points A and B.

The required thermodynamic conditions to render such a displacing of manganese possible are:

(1) The manganese activity and, thereby, its vapor pressure must be high in absolute value and compared to the corresponding values for iron and silicon.

(2) During the whole evolution of the alloy, the activities and, thereby, the vapor pressures of iron and silicon must remain low in absolute value and compared to that of manganese.

The theoretical study made by one of the applicants has proved:

(a) That, at 1327" C., said conditions are fulfilled and, besides, that the vapor pressures of iron and silicon remain substantially the same during a distillation, i.e., that the curve described by the composition of the residual alloy is a straight line passing through the vertex Mn and the initial point. Thus, if we want to distill a ternary alloy of composition represented by point M located in triangle MnAB, the evolution curve is the portion M'M which is entirely in the area of the homogeneous liquid phase.

([2) That, at temperatures near 1327 C., or no more than 200 to 300 from 1327 C., i.e., from 1027 C. to 1627 C. or from 1127 C. to 1527 C., the components activity may be determined from the indications obtained at 1327 C. by applying the formula .'1 R T 10g 0 which characterizes the solutions called regular in chemical thermodynamics words, and wherein R is the constant of perfect gases, T the absolute temperature,

- A the activity of component i at temperature T, and

N, the atomic fraction ofsaid component in the mixture.

(0) That the values of the manganese activity increase at any increase in temperature but that, within the previously indicated limits, the vapor pressures of iron and silicon remain near each other and are low when the temperature rises.

In consequence, Within the indicated temperature range, the evolution curves of the residue composition are straight lines passing through vertex Mn and the initial point.

Therefore, the best conditions of composition for the initial mixture, although they are not the only ones which may be utilized, are represented by all of the points comprised Within the triangle formed by vertex Mn and the two saturation points of the binary liquid Fe-Si at the temperature employed. Among the preferential utilization temperatures, the most favorable are those near 1327" C. because they ensure a broad enough triangular area and very low vapor pressures of iron and silicon. But, according to the invention, it is also possible to 3 operate at a higher temperature so as to maintain a ternary mixture, having its initial point outside triangle MnAB, in homogeneous liquid phase, until the manganese is completely removed. In this connection, we can give an indicative but not limitative example utilizing an initial ternary mixture represented by point N. The temperature must then be chosen near 1450 C., that is, slightly above thte melting point of compound FeSi represented by point N (1410 C.).

To realize the favorable conditions described hereabove, the process of the invention may utilize any mixture of silicomanganese orof ferro-silico-manganese with iron in the form of iron, steel or ferroalloys such as ferromanganese.

The amounts of iron or ferromanganese of given com position to be added to a given silicomanganese or to a given ferro-silico-manganese composition will be determined from the composition of said silicomanganese or ferro-silico-manganese.

As an exampie, if we have a terro-silico-manganese alloy having an atomic composition represented by point D and h": we want to completely remove the manganese therefrom by the action of iron at a temperature near 1327 C., it is preferable that the mixture subjected to distillation remain liquid until complete removal of manganese. In other words, that the points representing the progressive compositions of the ternary mixture remain inside triangle MnAB. As the addition of iron displaces the figurative point of the mixture along line DFe, the amount of iron to be added to bring said figurative point inside triangle MnAB onto portion AB', for instance to M, will be determined by the well-known rule of inverse segments. Likewise, if the iron is available as ferromanganese of such composition as represented by point B, the addition of said ferrornanganese to a ferro-silicomanganese of composition D would cause the figurative point of the mixture to move along line DE and the amount of ferromanganese to be added to bring the mixture inside triangle MnAB onto portion AB", for instance to M, would also be determined by applying the same known rule of inverse segments. If we want to use less iron or ferromanganese and bring the figurative point of the initial mixture to N for instance, or respectively to N, it will be necessary to heat to a higher temperature, 1450 C. for example, if we want to remove the manganese completely, or accept an incomplete removal of said manganese if a temperature below 1410" C. is desired.

The obtained manganese has an excellent purity which may be better than that obtained with known electrothermic or metallothermic processes and near that of electrolytic metal. in particular, it contains no more than 0.05% carbon, even it the initial material utilized is industrial silicomanganese or ferro-silico-manganese which often contains 1% carbon. The carbon present in the initial material remains in the residue, in particular as manganese carbide. Likewise, the Fe and Si contents of the obtained manganese may be lower than 0.1%. However, it higher Fe and Si contents are allowed, which is not objectionable in many metallurgical utilizations of manganese, the process may still be employed but, then, relatively high temperatures, for instance above 1600 C., or relatively low distillation pressures, for instance around 10- to mm. Hg, must be utilized.

As shown in the examples, the extracting and condensing values of manganese may reach 100% if, however, the temperature and composition conditions indicated as preferential are respected, i.e., under the conditions Where the liquid mixture subjected to distillation remains liquid until substantially complete removal of the manganese.

0n the other hand, the obtained ferrosilicon is a product of commercial value which, according to the applied conditions, may or may not contain small proportions of manganese. It may appear economical to adopt conditions under which complete removal of manganese is not realized. In particular, the residual alloy may be recovered in order to be used as a reducing agent for the production of ferro-silico-manganese. Thus, in practice, combining the invention process and the process of silicothermic reduction of oxidized manganese ores accomplishes a removal of manganese metal from said ores by addition of iron.

We indicate hereunder a non-limitative way of carrying out the invention which has been utilized to execute the following examples.

The crucible containing the mixture of silicomanganese and iron is placed in a distillation furnace wherein is realized, without any heating, a vacuum of about 10* mm. Hg. Then the enclosure is filled with argon carefully freed from nitrogen and the apparatus is evacuated again. Then the heating operation is carried out while the vacuum is maintained so as to ensure the degassing of the treated mixture and of the crucible and while the temperature rise is regulated so that the internal pressure is kept between 10 and 10* mm. Hg up to about l200-l250 C. At this temperature, the vacuum is increased to the predetermined value, generally around l0 mm. Hg and then the temperature is increased to obtain the distillation temperature for the pressure thus determined. The decomposition is efiected and the appearance oi: manganese on the furance condenser is indicated by a rapid decrease in pressure due to the working of the condensed metal as a trap. Generally, the operation does not last very long and, in particular, the operations cited as examples never exceeded 15 minutes. Then the heating is stopped and, once the furnace is sufiiciently cooled down, argon is introduced until the internal and external pressures are equal. Then the furnace is opened and the condenser removed; said condenser retains the manganese of basaltic structure absolutely similar to that of the metal obtained by the processes already described by applicants.

Example 1 The composition and origin of the raw materials were as follows:

(1) A soft iron containing 0.1% carbon. (2) A silicothermic silicomanganese alloy The composition of the charge, corresponding to point M on diagram of the figure, was the following:

Percent Silicomanganese 56.7 Soft Iron 43.3

Its weight was g. It was treated for 15 minutes at 1350 C. under a pressure of 5.10 mm. Hg.

The weights and compositions of the obtained prod ucts were as follows:

(1) Manganese distilled, then condensed, 54.4 g.

Percentages of elements other than manganese:

Percent Fe 0.08 Si 0.07 C 0.05

(.2) Residue, 92.2 g.

Percentage of residual manganese, 1.94% The condensation and extraction values of the manganese were respectively 91% and 97%..

Example 2 The composition and origin of the raw materials were as follows:

(1) A soft iron similar to the one used in Example 1. (2) A silicom-anganese alloy identical to the one used in Example =1.

The composition of the charge, corresponding to point N on diagram of the figure, was the following:

Percent Silicornanganese 75.5 Soft iron 24.5 Its weight was 150 g. It was treated for 15 minutes at 1450 C. under a pressure of 6.10 mm. Hg. The weights and compositions of the obtained products were as follows:

(1) Manganese distilled, then condensed, 74 g.

Percentages of elements other than manganese:

Percent Fe 0.075 Si 0.07 C 0.045

(2) Residue, 73 g. The condensation and extraction values of the manganese were respectively 92% and 98%.

The invention is not limited to the preferred embodi- 6 mentbut may be otherwise embodied or practiced within the-scope of the following claim.

We claim:

A process of simultaneously producing manganese metal and ferrosi'licon alloy, which comprises providing a mixture of silicomanganese alloy and iron, heating said mixture at a temperature at which the mixture becomes liquid, subjecting the liquid mixture to a pressure less than atmospheric pressure, distilling the manganese and continuing the operation at such a temperature that the mixture always remains in the homogeneous liquid state until the greatest part of the manganese hasbeen dis tilled, and condensing the manganese, said mixture having a composition which, when plotted on the isothermal triangular diagram MnFeSi, falls within the triangle of said diagram formed by the vertex Mn and the two saturation points of the binary liquid Fe-Si at the tem perature employed.

Ruelle Nov. 1-8, 1958 

